(1) Field of the Invention
The present invention relates to a device for minimizing earthquake shocks to a small building. More particularly, the invention relates to a seismic isolation device or a base isolation device for minimizing earthquake shocks to a small building such as a wooden house and a small steel-frame house.
(2) Description of the Prior Art
A conventional device for minimizing earthquake shocks to a small building comprises a foundation of the building being divided into an upper foundation and a lower foundation, perfect spherical bodies, such as steel balls and concrete balls, being rollably disposed between the upper foundation and the lower foundation, the perfect spherical bodies supporting the weight of the building including the upper foundation.
However, the above-mentioned device for minimizing earthquake shocks to a small building has the following disadvantages:
(i) The perfect spherical bodies have a very small coefficient of rolling friction. When the perfect spherical bodies are disposed between the upper foundation and the lower foundation, the building including the upper foundation is sensitively moved even by a small force of wind, etc. Therefore, a trigger device and a damping device are necessary. PA1 (ii) Since the perfect spherical bodies are very easily rolled, it is necessary to maintain the perfect spherical bodies in place by a precise means. PA1 (iii) Since the spherical bodies, such as concrete balls, cannot bear a large load, it is not possible to increase the weight per unit area of the building beyond a certain limit. PA1 (iv) Since the spherical bodies, such as steel balls, do not have satisfactory durability and weatherproofness, they cannot be used for a long period of time.